Conventionally, an electric vehicle is equipped with high-voltage batteries delivering a direct current to an inverter which transforms this direct current into an alternating current for powering an electric motor, the latter driving the movement of the vehicle.
To control the motor and in particular to control the switches of the inverter, it is necessary to know the angular position of the motor in order to power each phase of the motor at the right moment to obtain an optimum driving torque.
This is generally done by position sensors, for example Hall effect encoders/sensors, positioned on the rotation axis of the electric motor as is, for example, described in the document U.S. Pat. No. 6,307,336.
However, it appears that these position detectors are a weak point in the system and cause the vehicle to stop should the sensor fail. Furthermore, these sensors are expensive.
In the document EP 1564882, auxiliary windings are proposed to directly measure the electromotive force of each phase of the motor.
However, this solution leads to complex modifications to the electric motor.
Moreover, as for the position sensor, it is not known whether, for example, the absence of the measurement signal originates from a failure of this auxiliary configuration or from a failure of the motor itself.
The document U.S. Pat. No. 7,489,097 describes an electric system comprising an alternating current motor and a control inverter for directly measuring the electromotive force of the phases of the motor. For this, the inverter has to control the motor in a particular way so that the phase for which the EMF is to be measured is not powered during the measurement.
It happens that the trapezoidal control of the phases makes it possible to have two phases powered and one not powered. In this case, the current is zero during a period that is long enough to measure the EMF and detect its zero crossing.
However, this way is not appropriate for example for sinusoidal motor controls.